Polymers for use in optical devices

ABSTRACT

Optical devices fabricated from solvent processible polymers suffer from susceptibility to solvents and morphological changes. A semiconductive polymer capable of luminescence in an optical device is provided. The polymer comprises a luminescent film-forming solvent processible polymer which contains cross-linking so as to increase its molar mass and to resist solvent dissolution, the cross-linking being such that the polymer retains semiconductive and luminescent properties.

This application is a Divisional of application Ser. No. 08/875,049,filed Jun. 24, 1997 now abandoned, which is a 371 of PCT/GB95/03043,filed Nov. 28, 1995, which application is incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to polymers for use in optical devices such asphotoluminescent and electroluminescent devices.

BACKGROUND TO THE INVENTION

Polymer LEDs were first described by Burroughes et al (PCT GB90/00584).Devices based on copolymers (Holmes et al, PCT GB91/01420; PCTGB91/01421) multilayers (PCT GB93/01573; PCT GB93/01574) and with highelectron affinity polymers have also been reported (PCT GB94/01118).

Conjugated poly(3-alkylthienylene)s have been prepared, and reviewed byJ. Roncali (Chem Rev, 1992, 92, 711) and applications inelectroluminescent devices were reported by Y. Ohmori et al. (Jpn, J.Appl. Phys. Part 2, 1991 20(11B), L1938-1940. Regioregularpoly(3-alkylthienylene) s have been described by R. D. McCullough, R. D.Lowe, M. Jayaraman, and D. L. Anderson, (J. Org. Chem., 1993, 58, 904).Solvent dependent chiroptical behaviour has been reported forregioregular poly (3-alkylthienylene) s M. M. Bouman, E. E. Havinga, R.A. J. Janssen and E. W. Meijer, Mol. Cryst. Liq. Crist., 1994, 256,439). Regiorandom hydroxy-functionalised polythiophene copolymers havebeen reported (C. Della Casa, E. Salatelli, F. Andreani and P. CostaBizzarri, Makromol. Chem. Makromol. Symp.,1992, 59, 233), and thepotential for cross linking was noted (J. Lowe and S. Holdcroft, Polym.Prepr., 1994, 35, 297-298).

More advanced polymeric LEDs can involve the use of both emissive andcharge transport materials in order to improve the efficiency of thedevice [P. L. Burn, A. B. Holmes, A. Kraft, A. R. Brown, D. D. C.Bradley, R. H. Friend, Mat. Res. Soc. Symp. Proc., 1992, 247, 647; A. R.Brown, D. D. C. Bradley, J. H. Burroughes, R. H. Friend, N. C. Greenham,P. L. Burn, A. B. Holmes and A. Kraft, Appl. Phys. Lett., 1992, 61,2793; T. Nakano, S. Doi, T. Noguchi, T. Ohnishi Y. Iyechika, SumitomoChemical Company Limited, U.S. Pat. No. 5,317,169, May 31, 1994].Emissive polymers are the main active layer in polymer LEDs. Singletexcitons are formed under double charge injection which then decayradiatively to produce light emission. On the other hand, chargetransport polymers have also been found to play an important role inenhancing the internal quantum efficiency of devices (photons emittedper electron injected), decreasing working voltages and in increasingthe life-time of the device. This was fist shown by use of the knowncharge transporting molecule (PBD)[2-(4-biphenyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole] as a blend inpoly(methyl methacrylate) as mentioned above [Burn et al.; Nakano etal.]. Recently, high efficiency (4%) blue electroluminescence has beenachieved by means of charge-transporting layers using polyvinylcarbozole(PVK) as a hole-transporting material and PBD blended with poly(methylmethacrylate) (PMMA) as an electron transporting material in themulti-layer device [ITO/PVK/PQ (polyquinoline)/PBD+PMMA/Ca] [I. D.Parker, Q. Pei, M. Marrocco, Appl. Phys. Lett., 1994, 65(10), 1272]. Therole of the charge transport layer in LEDs include: (i) assistingeffective carrier injection from the electrode to the emitting layer(ii) confining the carriers within the emitting layer and thusincreasing the probability of recombination processes through radiativedecay, leading to light emission (iii) preventing the quenching ofexcitons at the boundary between an emitting material and the electrode.

Most common conjugated polymers are more easily p-doped and thus exhibithole-transport properties. On the other hand, electron transport andelectron injection in polymer LEDs have proved to be more difficult andare thus required in order to improve device efficiency and performance.

An aromatic oxadiazole compound such as PBD is well known to be a usefulelectron transport material [K. Naito, Jpn. Kokai Tokkyo Koho, JP05,202,011,1993; S. Lunak, M. Nepras, A. Kurfurst and J. Kuthan, Chem.Phys., 1993, 170, 67]. Multi-layered LED devices with improvedefficiency have been reported using evaporated PBD or a spin-coatedPBD/PMMA blend as an electron transport layer.

In each case, however, problems that will lead to device break-down(such as the aggregation and re-crystallisation of PBD) may be expectedto occur under the influence of an electrical field or temperatureincrease when the device is working [C. Adachi, et al, Jpn. J. Appl.Phys., 1988, 27, L269; C. Adachi, S. Tokito, T. Tsutsui, S. Saito, Jpn.J. Appl. Phys.1988, 27, L713; Y. Hamada, C. Adachi, T. Tsutsui, S.Saito, Jpn. J. Appl. Phys. 1992, 31, 1812; K. Naito, A. Miura, J. Phys.Chem., 1993, 97, 6240].

Conjugated polymers that contain aromatic and/or heteroaromatic ringshave enjoyed considerable interest because of their potential electricalconductively after being doped and electroluminescent properties.However, there is a severe processibility problem for conjugatedpolymers as they are usually insoluble or infusible because of therigidity of the main polymer chain and strong intermolecular forcesbetween polymer chains. One way to improve the processibility of thesepolymers is to prepare a soluble precursor which can then be convertedinto a rigid conjugated polymer, as can be done withpoly(p-penylenevinylene) (PPV) (A) [A green yellow emitter, prepared bythe sulfonium precursor route: P. L Burn, D. D. C. Bradley, R. H.Friend, D. A. Halliday, A. B. Holmes, R. W. Jackson and A. Kraft, J.Chem Soc., Perkin Trans., 1992, 1, 3225]. Another way is to generate afully conjugated material while increasing solubility by attaching bulkyand flexible alkyl or alkoxy groups onto the main chain therebyweakening the intermolecular forces (as shown in the case of alkyl—oralkoxy-substituted PPV in (B) and (C)). A third way is to attach orinsert a photoluminescent chromophore to a flexible polymer chain sincethe flexible chain segments will enhance the solubility in conventionalorganic solvents. This has been shown in the case of a block copolymerconsisting of π-conjugated active blocks sandwiched between non-activeflexible blocks [R. Gill, G. Hadziioannou, J. Herrema, G. Malliaris, R.Wieringa, J. Wildeman, WPI Acc. . No.94-234969; Z. Yang, I. Sokolik, F.E. Karasz, Macromolecules, 1993, 26(5), 1188Sumitomo Chem. Co. Ltd., JP5320635].

In order to improve the performance of polymer LEDs, the luminescentpolymer needs to be used in association with a charge transport polymer.Conventionally, charge transport materials may be used as single layersbetween the emitting layer and the electrodes. Alternatively, blends maybe used.

Thus, prior art polymers used in optical devices suffer fromsusceptibility to solvents and morphological changes owing to low glasstransition temperatures. Moreover, when molecular electron transportmaterials are used in such optical devices, problems involving theaggregation and recrystallisation of the material may lead to devicebreakdown.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a semiconductive polymercapable of luminescence in an optical device, such as a photoluminescentor electroluminescent device. The polymer comprises a luminescentfilm-forming solvent processible polymer which contains cross-linking soas to increase its molar mass and to resist solvent dissolution, thecross-linking being such that the polymer retains semiconductive andluminescent properties.

By increasing the molar mass of the polymer the deleterious effects ofsusceptibility to solvents and morphological change owing to low glasstransition temperatures are avoided. Surprisingly, the cross-likedpolymers retain their semiconductive and luminescence properties.Luminescent and electroactive polymer thin films such as those used inoptical devices may therefore be stabilised. Because the thin filmsresist dissolution in common solvents this enables deposition of furtherlayers of, for example, electroactive polymer films by solvent coatingtechniques thereby facilitating device manufacture. The cross-linkedsemiconductive polymers retain all their desirable luminescenceproperties and have the advantage of exhibiting enhanced morphologicalstability under device operation.

The cross-linking may be formed in the semiconductive polymer by thermalcross-linking, chemical cross-linking or photochemical cross-linking.Cross-linking methodology for polymers is well-known. For example, thecross-linking of polymers for photoresists by thermal, chemical andphotochemical methods have been reviewed; (S. Paul, Cross LinkingChemistry of Surface Coatings, in Comprehensive Polymer Science, G.Allen (Ed.), Pergamon, Oxford, 1989, Vol. 6, Ch. 6, pp. 149-192; S. R.Turner and R. C. Daly, Photochemical and Radiation-sensitive Resists, inComprehensive Polymer Science, G. Allen (Ed.), Pergamon, Oxford, 1989,Vol. 6, Ch. 7, pp. 193-225; S. P. Pappas, Photocrosslinking inComprehensive Polymer Science, G. Allen (Ed.), Pergamon, Oxford, 1989,Vol. 6, Ch. 5, pp. 135-148). In addition, an example of cross linking ofpolymers through ring opening metathesis polymerization ofcyclooctene-5-methacrylate was reported by B. R. Maughon and R. H.Grubbs, (Polym. Prepr., 1995, 36, 471-472).

A particularly useful example of thermal cross-linking involves the useof azide groups usually attached to the polymer main chain by a spacergroup. At a temperature typically in the range of 80° C. to 250° C. thealiphatic azide will either form a pyrazoline adduct with a double bondor decompose to form a highly reactive nitrene which can then formcross-links with other polymers. An aryl azide will behave similarly inthe range 20° C. to 250° C. The spacer is advantageously non-rigid.Preferably the spacer comprises —(CH₂)_(n)— or —(CH₂)_(n)—Ar— in which nis an integer preferably in the range 2 to 20 and Ar is an aryl group,preferably a phenylene group. A good example of such a spacer is a—(CH₂)₁₁— group.

Chemical cross-linking may be effected using diisocyanates or activateddicarboxylic acid derivatives to react with terminal functional groups(e.g. —OH) on the soluble polymer. In this way urethane or esterlinkages can be created. Alternatively, a low molecular weightbifunctional or polyfunctional compound (e.g. an epoxy resin) can beblended with the solvent processible polymer for the purpose of reactingchemically with existing functional groups (e.g. amino etc) in thepolymer main chain or on the side chains of the polymer. Suitablecross-linking agent include formaldehyde or other aldehydes, bis orpolyfunctional azides such as 1,6-bisazidohexane, and polyisocyanates.

Photochemical cross-linking may be effected by any side chainsubstituent capable of becoming activated upon irradiation with light ofappropriate energy, usually UV light. For example, cinnamate esters willundergo [2+2]-cycloaddition under appropriate conditions, typicallyirradiation of the polymer film at ambient temperature with a mediumpressure Hg lamp. Also, photolysis of alkyl or aryl azides over a widetemperature range, preferably −50° C. to +50° C., can generate reactivenitrene intermediates which can cross-link the polymer.

The luminescent film-forming polymer and the cross-linked form thereofaccording to the present invention may be luminescent either by virtueof a luminescent main chain or a luminescent side chain. The polymer maycomprise any such film-forming polymer, including copolymers andoligomers. The luminescent main chain polymers have been described inPCT GB 90/00584 and PCT GB91/01420, for example. Such polymers includepoly (arylene vinylene) derivatives. Particularly useful poly(arylenevinylene) polymers in the present invention include polymers ofgeneral formula B and which carry cross-linkable functionality as anattachment. electroluminescent polyarylenes are also particularly usefulin the present invention, including polyheteoarylenes, especially thepolythiophenes. Polythiophene copolymers are known to be capable ofluminescence and substituted poly(3-alkyl thienylenes) are preferred.

Statistical copolymers of substituted poly(3-alkylthienylene) scontaining regioregular head to tail linkages can be made according toK. A. Murray, S. C. Moratti, D. R. Baigent, N. C. Greenham, K. Pichler,A. B. Holmes and R. H. Friend, in Snyth. Met., 1995, 69, 395-396 andthen cross-linked. The side chain alkyl substituents or a fractionthereof carry functionality which can be employed in chemical,photochemical or thermal cross-linking processes.

Further examples of polymers having a luminescent main chain are thosewhich have the electroluminescent segments in scheme 2 below formingpart of the polymer main chain. In a preferred embodiment of theinvention, the polythiophene copolymer is of the general formula

in which R′ is a solubilising group, R″ is a spacer group cross-linkingthe main chain to another polymer, and x, y and n are each integers,wherein x:y is in the range 19:1 to 1:2 and n is in the range 3 to 100.

Preferably, R′ is —C₆H₁₃.

Where the polymer includes a luminescent side chain, this side chain mayincorporate any luminophoric group such as a species containing at least3 unsaturated units in conjugation. Preferably the luminescent sidechain comprises a distyryl benzene. Where the polymer includes aluminescent side chain, there is no need for the main chain of thepolymer itself to be luminescent but the polymer should be transparentto the emitted light. Various polymers may therefore be used to form themain chain. Especially useful polymers include polystyrenes,polyacrylates, polysiloxanes, and polymethacrylates which are preferred.Polymethacrylates are discussed in further detail below.

In one embodiment of the invention, the polymer further comprises acharge transport segment which is present in the polymer main chain orcovalently linked thereto in a charge transport side chain.

In a further aspect of the invention a polymer is provided which iscapable of charge transport, preferably electron transport, in anoptical device such as an electroluminescent device. The polymercomprises a film-forming polymer which is solvent processible or formedfrom a processible precursor polymer and which includes a chargetransport segment in the polymer main chain or covalently linked theretoin a charge transport side chain.

The polymers may be used as both charge transporting and/orelectroluminescent materials in polymer light emitting devices. Thepolymers may therefore include charge transport functional segments andelectroluminescent functional segments either as a side chain group orin the main chain of the polymer. Precursor polymers leading, after aconversion step, to intractable final polymers may be used, as well asfully processible polymers. Each type of polymer can have specificadvantages in processing multi-layered structures.

The charge transport segment may comprise the moiety Ar₁—Hwet—Ar₂inwhich Ar₁ and Ar₂ are the same or different from one another and arearomatic units. Examples of these aromatic units are set out below inScheme 1. Het is a heteroaromatic ring, the electronic structure ofwhich favours charge transport. Examples include oxidiazole,thiadiazole, pyridine, pyrimidine and their benzo-fused analogues suchas quinoline. Heteroaromatic rings which are electron deficient andtherefore enhance charge injection and transport are generally useful.

Ar₁, Ar₂ are aromatic, heteroaromatic, fused aromatic derivativesthereof, or double bonds:

R₁₋₁₉ and R₁₋₁₂ are groups selected from the groups consisting ofhydrogen and halogen atoms and cyano, alkyl and alkoky side chains.

Scheme 1 Representative charge transport segments

Scheme 2 Representative Electroluminescent Segments

The electroluminescent segments may comprise conjugated photoluminescentchromophore segments as illustrated in Scheme 2.

The side chain (co)polymer consists of any backbone polymer containingside chain modifications with luminescent and/or electron transportingsegments. A typical example is a poly(methacrylate) that contains chargetransport segments and/or luminescent segments in the pendant side groupas shown in Scheme 3.

The side chain polymer may contain an optional third functional segmentthat will play a cross-linking role so as to improve the stability ofthe poly(methacrylate) i.e. by raising the glass transition temperature(t_(g)). The third segment may be a chemically cross-linkable group suchas an epoxide, a thermally cross-linkable group such as an azide, or aphotocross-linkable group such as a cinnamate or a stilbene group.

Scheme 3 Illustration of a side chain copolymer (usingpoly(methacrylate) as an example)

The main chain polymers and copolymers referred to herein are (co)polymers that contain transport segments and/or electroluminescentsegments along the polymer or copolymer backbone with or withoutflexible spacers as illustrated by a representative example in Scheme 4.

The polymers described in the present invention are particularlysuitable for use as electron transport layers in a multilayer LED deviceeither as a blend with another electroluminescent polymer or as one ofthe components in a copolymer with another electroluminescent segment.This improves both the internal quantum efficiency and deviceperformance.

Scheme 4 Representative Main Chain Polymer Structures

Scheme 5: Synthesis of oxadiazole monomers

PREPARATION AND APPLICATION OF SIDE CHAIN POLYMERS

Poly (methacrylates) have many advantages such as high transparency,high resistance to chemicals, and good mechanical strength. It is alsorelatively easy to synthesise high molecular weight polymers as well asmulti-functional copolymers.

To illustrate this general concept, a range of aromatic oxadiazolebonded polymers [especially poly(methacrylates)] have been synthesisedand investigated incorporating monomers as shown in Scheme 5. These(co)polymers can be used in association with emissive polymers indifferent ways (single layer, blended layer and copolymer layer) to givedevices with improved performance.

Scheme 6 A Poly(methacrylate) Containing a Blue Light Emitting SideChain

In a previous patent application (PCT/GB93/02856) a range ofpoly(methacrylate) derivatives containing chromophores D featuring blueemission were synthesised. The chromophoric groups F,G,H,I comprised twoor three conjugated aryl rings (distyrylbenzene units) attached to thepoly(methacrylate) chain via covalent linkages. This is a representativeexample of the numerous possibilities for blue side chain modified lightemitting polymers. Crosslinking and copolymerisation with polymerscarrying charge transporting segments make these materials particularlyattractive candidates for blue light emission.

The polymer capable of charge transport is generally used in an opticaldevice as a functional polymer layer between an electroluminescentpolymer layer and a charge injection electrode. This layer plays a rolein enhancing charge and especially electronic injection from the metalelectrode (usually a cathode) and charge transport. The polymer maybalance the charge injection in a multi-layer polymer LED withimprovement of device performance.

In a further aspect, the present invention provides use of a polymer asdescribed above in an optical device, preferably an electroluminescentdevice. The present invention also provides an optical device whichcomprises a substrate and a polymer as defined above supported on thesubstrate. The optical device is preferably an electroluminescentdevice. Typically, the polymer is used in such devices as a thin film.In operation the cross-linked semiconductive polymers retain desirableluminescent properties and have the advantage of exhibiting enhancedmorphological stability.

The present invention will now be described in further detail, by was ofexample only, with reference to the accompanying drawings in which:

FIG. 1 shows a graph of internal quantum efficiency against current forthe devices ITO/PPV/PMA−PPD/Ca and ITO/PPV/Ca;

FIG. 2 shows a graph of current against field for the devices of FIG. 1;

FIG. 3 shows a graph of luminance L against voltage V for the deviceITO/PPV/PMA−TPV+PMA−PPD/Ca;

FIG. 4 shows a graph of efficiency against current for the device ofFIG. 3;

FIG. 5 shows a graph of luminance against wavelength lambda for thedevice ITO/PPV/PMA−TPV+PMA−PBD/Ca;

FIG. 6 shows a graph of current against voltage for the deviceITO/PPV/PMA−TPV−PBD/Al;

FIG. 7 shows a graph of luminance against wavelength lambda for variousLED devices ITO/PPV/Ca, ITO/PPV/Copolymer of 16 and 9 b (1:1)/Alindicating cross-linking of the distyrlbenzene chromophore as a functionof time;

FIG. 8 shows a graph of efficiency against current for the deviceITO/PPV/copolymer/Al of FIG. 7;

FIG. 9 shows a graph of luminance against wavelength lambda for thecopolymer device of FIG. 7;

FIG. 10 illustrates representative polythiophenes for cross-linking;

FIG. 11 shows cross-linking of a 9:1 copolymer 45 b before and afterheating;

FIG. 12 shows a graph of a UV-VIS absorption spectrum of copolymer 49;

FIG. 13 shows a photoluminescence spectrum of polymethachrylate 49(p=0.5, q=0.3, r=0.2) with three functional groups;

FIG. 14 shows a UV-VIS absorption spectrum of the 3-unit copolymer ofFIG. 13 upon exposure to UV light as a function of time;

FIG. 15 shows an electroluminescent spectrum of a light emitting deviceusing polymer 49 as an emissive layer (ITO/polymer 49/Ca, with internalquantum efficiency of 0.1%);

FIG. 16 shows graphs of current and luminance against voltage for across-linked polythiophene (45 b, 9:1) device; and

FIG. 17 shows an electroluminescent spectrum of a cross-lined thiophenedevice of FIG. 16.

EXAMPLE 1

The Synthesis of Methacrylate-PPD Monomer (9 a) —Scheme 5

Preparation of aldehyde (2)

Sodium borohydride (4.9 g, 0.13 mol) pellets were added to a solution ofterephthaldehyde mono-(diethyl acetal) (39.9 g, 0.19 mol) in MeOH (150ml) at 0° C. (using an ice bath). The reaction mixture was stirred for1.5 h at 0° C. Water (100 ml) and HCl (10M, 200 ml) were added and themixture stirred at room temperature for 1.5 h. After removing MeOH underreduced presure, ethyl acetate (200 ml) was added. The organic layer waswashed with sodium hydrogen carbonate solution and water. The clearorganic layer was dried with anhydrous sodium sulfate. The crude product(20.35 g) was recrystallized from chloroform/hexane and was obtained asfine crystals(18.79 g 73%); m.p. 43-45° C.

Preparation of 4-(acetyloxy-methyl)benzoic acid (3):

Triethylamine (15.4 ml, 110.4 mmol) was added to a solution of aldehyde(2) (12.57 g, 92.4 mmol) in THF (50 ml) and cooled to 0° C. Acetylchloride (7.91 g, 110.4 mmol) was then gradually added over 25 minutes,and the mixture was then left to stir for two hours at room temperature.After one hour, ethyl acetate (200 ml) was added and the solution washedwith sodium carbonate (100 ml), HCl (17%, 50 ml) and water (100 ml)respectively. The organic layer was then dried over sodium sulfate andthe solvent removed under reduced pressure to give an oil whichcrystallised when cooled. Re-crystallisation in methanol-hexane gavelight yellow crystals.

4-[acetyloxy-methyl]benzaldehyde:

(15.39 g, 94%). m.p. 33-35° C.; R_(f)0.62(ether). v_(max) (KBr)/cm⁻¹:1735 s (O−C=O), 1686 s (H−C=O), 1608 m (phenyl absorption), 1384, 1369,1253, 1212, and 811; λ_(H)(250 MHz, CDCl₃) 2.10 (3 H, s CH₃), 5.14(2 H,s, CH₂O—), 7.41 (2 H, d, J 8.1, Ar—H), 7.89(2 H, d, J8.1, Ar—H) and9.98(1 H, s, CHO). δ_(C)(63.5 MHz; CDCl₃) 20.8(CH3), 65.4(CH₂), 128.2,129.9, 142.7, 141.8(phenyl carbons), 170.6(O−C=O) and 191.8(H−C=O).

4-[acetyloxy-methyl]benzaldehyde (15.3 g, 86.5 mmol) in acetone (250 ml)was then reacted with Jones reagent (33.0 ml, a three-fold excess) whilestirring (exothermal reaction). This was stirred for 2 h beforefiltering out the green solid. The green solid as then dried underreduced presure and dissolved in ethyl acetate (400 ml) and washed withsodium carbonate solution and water until neutral. After removal ofsolvent, a crop of yellow crystals (13.3 g) was obtained which was thenrecrystallised in chloroform-hexane to give a white crystal (3) (12.62g, 76%). m.p.120-123° C.; R_(f)0.29(1:1 Hexane-ether v/v).

Preparation of 4-tert-butyl benzoic hydrazide (5a):

Hydrazine hydrate (9.4 ml, 194 mmol) was added to methyl 4-tert-butylbenzoate (25.3 g, 29 mmol) in ethanol (25 ml) and then refluxed undernitrogen for 18 h. The solvent was then removed under reduced pressureand the solid residue recrystallised from hot toluene-hexane (140 ml,10:4 toulene-hexane v/v), to give colourless crystals of 4-tert-butylbenzoic hydrazide (19.25 g, 76%). m.p.126-128° C.

Preparation of 1-(p-tert-butylbenzoyl)-2-(4-acetyloxy-methyl-benzoyl)-hydrazine (6):

Thionyl chloride (30 ml) was added to (3) (15.10 g, 77.8 mmol) in a 250ml three-neck RB flask and refluxed for 40 minutes at 70-80° C. Afterremoving the excess thinoly chloride under vacuum, the brown oil (4) wasthen washed with chloroform (3×15 ml). The residue was then dissolved indry pyridine (120 ml). Hydrazide (5a) (14.9 g, 77.8 mmol) was at lastadded. The brown solution was stirred and refluxed for 3 h beforepouring the mixture into ice water (700 ml) to precipitate the productwhich was then washed with water and dried at 80° C. in vacuo to givethe product. The product can be further purified by recrystallisation intoluene to give white crystals. m.p. 229-230° C. (with liquid crystalbehaviour and easy decomposition in air); δ_(H)(250 MHz, CDCl₃) 1.32(9H, s, ^(t)Bu), 2.13(3 H, s, CH₃CO), 5.13(2 H, s, CH₂), 7.41(4 H, t) and7.81(4 H, m, Ar-H), 9.59 and 972(2 H, d, —NHNH—); δ_(c)(63.5 MHz, CDCl₃)20.9(CH₃), 31.1(C(CH₃)₃), 65.4(CH₂), 125.7, 127.1, 127.6, 128.0, 128.3,130.4, 131.1, 140.5(C), 156.1(C=O), 163.9(C=O); v_(max)(CHCl₃)/cm⁻¹:3233(N-H), 1736(O-CO), 1672(NH-CO), 1633, 1445, 1450(phenyl absorption);[Found: C, 68.66; H, 6.64; N, 7.65C₂₁H₂₄N₂O₄requires C, 68.48; H, 6.52;N, 7.61%].

Preparation of2-(para-tert-butyl-phenyl)-5-(4-acetyloxy-methyl-phenyl)-1,3,4-oxadiazole(7a):

POCl₃ (35 ml) was added to (6a) 3.31 g, 8.99 mmol) and refluxed for 18 hunder nitrogen. POCl₃ was distilled from the reaction mixture beforepouring the residue into ice water. Extraction with ethyl acetate (2×200ml) gave a yellow oil after removal of solvent. The crude product (TLCshowed 3 spots) was purified by flash column chromatography usinghexane-ether (10:1 to 3:7 v/v) yielding colourless crystals (7a) (1.02g, 22%). m.p. 93-95° C.; R_(f)0.24 (1:1 hexane-ether v/v); δ_(H ()250MHz, CDCl₃) 1.36(9 H, s, ^(t)Bu), 2.14(3 H, s, CH₃CO), 5.18(2 H, s,CH₂), 7.54 and 8.07 (4 H, m, Ar-H); σ_(c)(63.5 MHz, CDCl₃) 21.0 (CH₃CO),31.1 (C(CH₃)₃), 35.1 (C(CH₃)₃), 66.5 (CH₂), 121.1 and 126.1, 126.8,139.7(Ar-CH₂OAc), 123.9, 127.1, 128.6, 155.5(Ar-^(t)Bu), 164.1(C) and164.8 (C) and 170.7 (C=O); [found: C, 72.12; H, 6.29; N, 8.10. C₂₂H₂₂O₃Nrequires C, 72.0; N, 8.0; H, 6.3%]; m/z (EI) 350 (80), 335 (100%), 161(30) and 43 (30) [Found: (M⁺⁾ 350.1630. C₂₁H₂₂O3N requires M, 350.1630].

Preparation of2-(para-tert-butyl-phenyl)-5-(4-hydroxyl-methyl-phenyl)-1,3,4oxadiazole(8a)

Oxadiazole (7a) (0.67 g, 191 mmol) was added to a solution of sodiumhydroxide (0.11 g, 2.75 mmol) in ethanol (30 ml), and the mixturestirred for 2 h. The mixture was poured into aqueous sodium bicarbonate(5%, 100 ml) and a white precipitate which formed, was collected byfiltration. The crude product (0.9 g) was recrystallised fromCHCl₃-hexane yielding colourless crystals (8a) (0.53 g, 91%). m.p.115-116° C.; R_(f) 0.08 (1:1 hexane-ether v/v). ν_(max)(CHCl₃)/cm⁻¹;3308(OH), 2967(CH), 1615, 1552, 1495(Ar), 965(oxadiazole); δ_(H)(250MHz, CDCl₃) 1.36 (9 H, s, (C(CH₃)₃), 2.22 (1 H, t, OH), 4.79 (2 H, d,CH₂O), 7.53 and 8.06 (8 H, m, 2×Ar—H); d_(C) (63.5 MHz, CDCl₃) 21.0(CH₃CO), 31.1 (C(CH₃)₃), 35.1 (C(CH₃)₃), 64.5 (CH₂OH), 121.0 and 123.1(aryl carbons bonded to oxadiazole ring), 126.1, 126.8, 127.1,127.3(Ar), 144.7.0 (Ar—CH₂OH), 155.4 (Ar—^(t)Bu), 164.1 and 164.8 (C);[Found: C, 74.08; N, 9.03; H, 6.52; C₁₉H₂₀O₂N₂ requires C, 74.0; N, 9.1;H, 6.5%]; m/z (EI) 308 (55), 293 (100%), 161 (25) 135 (25), 116 (25) and77 (25) [Found: (M⁺) 308.1525. C₁₉H₂₀O₂N₂ requires M, 308.1525].

Preparation of monomer (9a)

Triethylamine (1.0 ml, 41.0 mmol) was added to a solution of oxadiazole(8a) (0.61 g, 19.8 mmol) in THF (20 ml) and stirred under N₂.Methacryloyl chloride (0.9 ml, 84 mmol) was added slowly by syringe. Thesolution was stirred for 2 h at room temperature. Cloudiness wasobserved. Ether (100 ml) was added and the mixture was washed with water(100 ml), HCl (2M, 100 ml), and brine (100 ml). The combined aqueouswashings were then extracted with more ether (100 ml). The combinedether layers were dried over anhydrous sodium sulfate and the solventremoved under reduced pressure to give an off-white solid. R_(f)=0.38(1:1 hexane-ether v/v). After purification using flash columnchromatography with ether-hexane(1:1 v/v), and drying, (8a) was obtainedas colourless crystals (0.67 g, 91%). m.p. 106-109° C.;ν_(max)(CHCl₃)/cm⁻¹: 2966(C—H), 1720 s (C═H), 1615, 1494(Ar),965(oxadiazole); δ_(H)(250 MHz, CDCl₃) 1.36 (9 H, s, ^(t)Bu), 1.99 (3 H,t, J 1.313, CH₃), 5.27 (2 H, s, CH₂), 5.63, 6.20 (2 H, 2, CH═CH), 7.55and 8.10 (8 H, m, 2×Ar—H); XXXδ_(c) (100 MHz, CDCl₃) 18.3 (CH₃), 31.1(C(CH₃)₃), 35.1 (CMe₃), 65.7 (CH₂—O), 121.0 and 123.8 (Ar), 126.1,126.2, 126.8, 127.1, 128.4, 139.8 and 155.5 (Ar), 164.0 and 164.7(carbons in the heterocycle), and 167.0 (C═O); [Found: C, 73.40; H,6.35; N, 7.50; C₂₃H₂₄O₃N₂ requires C, 73.4; H, 6.4; N, 7.4%]. m/z (EI)376 (80), 361 (100%), 161(40), 69(40) and 41(65) [Found: (M⁺) 376.1787,C₂₃H₂₄O₃N₂ requires M, 376.17868].

EXAMPLE 2

The Synthesis of Methacrylate Monomer PBD (9b)

Synthesis of1-(4-phenyl-benzoyl)-2-(4-acetyloxyl-methyl-benzoyl)-hydrazine (6b):

The synthesis is similar to that of (6a) except hydrazide (5b) was usedinstead of hydrazide (5a). After isolating the clay-like solid, it wasrecrystalised in 95% ethanol and dried at 100° C. under vacuum to givewhite crystals (6b) (88%). R_(f) 0.28 (ether); δ_(H) (250 MHz, CDCl₃)2.13 (3 H, s, CH₃), 5.15(2 H, s, CH₂), 7.44 (5 H, m, Ar—H), 7.65, 7.92(8 H, m, Ar—H); δ_(C) (63.5 MHz, CDCl₃) 20.9 (CH₃), 65.4 (CH₂), 127.2,127.8, 128.0, 129.0, 130.0, 131.0 (Ar), 139.8 (Ar—Ph₂), 140.5 (CC═O),145.1 (CCH₂), 164.7(C═O), 170.7 (C═O). ν_(max) (chloroform)/cm⁻¹: 3407,3234(N—H), 3013(C—H), 1736(CO—O), 1635, 1448(Ar), 965 (oxadiazole).[Found: C, 69.8; H, 5.1; N, 7.0; C₂₅H₂₀N₂O₃ requires C, 71.11; H, 5.19;N, 7.21%].

Synthesis of 2-(biphenyl)-5-(4-acetyloxy-methyl-phenyl)-1,3,4-oxadiazole(7b):

The cyclodehydration of (6b) to form (7b) is similar to the preparationof (7a). Thus, (6b) (11.95 g, 30.76 mmol) was dissolved in POCl₃(40 ml).After refluxing for 6 h, POCl₃ was removed by distillation beforepouring the residue into ice water to obtain a light grey powder whichwas then washed with water (5×200 ml) until neutral. The crude productwas purified by flash column chromatography using hexane-ether (1:1,v/v). (7b) was obtained as colorless crystals (5.57 g, 40%).m.p.130-132° C.; R_(f) 0.71(ether); δ_(H) (250 MHz, CDCl₃) 2.16 (3 H, s,CH₃), 5.20 (2 H, s, CH₂), 7.50, 7.72 and 8.22(13 H, m, Ar—H), δ_(c)(63.5 MHz, CDCl₃) 20.9 (CH₃CO), 65.5 (CH2), 122.6, 123.7(C-oxadiazole),127.1, 127.3, 127.4, 127.7, 128.2, 128.6, 129.0 (Ar), 139.8, 144.6(C—Ph), 164.3, 164.6(oxadiazole), 170.7 (C═O); ν_(max)(chloroform)/cm⁻¹: 3013(C—H), 1737(CO—O), 1614, 1550, 1484(Ar),965(oxadiazole). [Found: C, 74.76; H, 4.75; N, 7.54; C₂₃H₁₈N₂O₃ requiresC, 74.58; H, 4.90; N, 7.56%].

Synthesis of 2-biphenyl-5-(4-hydroxyl-methyl-phenyl)-1,3,4-oxadiazole(8b):

(7b) (7.0 g, 18.9 mmol) and sodium hydroxide(1.33 g, 33.3 mmol) weredissolved in ethanol (95%, 350 ml) and stirred at room temperature for 3h before pouring the reaction mixture into sodium carbonate solution(600 ml) to obtain a white precipitate. The product was then dissolvedin ethyl acetate, washed with water(3×300 ml) and dried with anhydroussodium sulfate. The solvent was evaporated off and drying in vacuoyielded (8b) as fine white crystals (5.6 g, 90%). m.p.168-171° C.; R_(f)0.71 (ether); δ_(H) (250 MHz, CDCl₃) 2.25(1 H, br, OH), 4.81(2 H, s,CH₂), 7.48(5 H, m, Ar—H), 7.70(4 H, m, Ar—H) and 8.15(4 H, m, Ar—H);δ_(c) (63.5 MHz, CDCl₃) 64.7 (CH₂), 122.7, 123.1 (C-oxadiazole), 127.2,127.4, 127.7 128.2, 129.0 (Ar), 139.8, 144.5 and 144.9 (C—Ph, CCH₂),164.5 (oxadiazole); ν_(max) (CHCl₃)/cm⁻¹: 3692, 3610(OH), 3015(H bondedOH), 1614, 1551 1484(Ar), 965(oxadiazole). [Found: C, 76.87; H, 4.75; N,8.27. C₂₁H₁₄N₂O₂ requires C, 76.81; H, 4.91; N, 8.54%].

Synthesis of methacrylate PBD monomer (9b):

(8b) (3.86 g, 11.76 mmol) was dissolved in dry THF (150 ml) and drytriethylamine (12 ml, 0.49 mol), and stirred at 0° C. Methacryloylchloride (3 ml, 0.28 mol) was then added dropwise with a syringe. Afterstirring for 2 h and then, warming up to room temperature, the cloudysolution was poured into ice water (600 ml) to get a white precipitatewhich was washed with water (5×150 ml) and then, dried to obtain themonomer (9b). TLC showed mainly one spot, R_(f) 0.38 (1:1 44ether-hexanev/v). The crude monomer was then further purified with flash columnchromatography using ether-hexane. (9b) was obtained as white crystals(3.78 g, 81%). m.p.123-125° C. (possible polymerisation). δ_(H) (250MHz, CDCl₃) 2.01(3 H, s, CH₃), 5.29(2 H, s, CH₂), 5.64(1H, s, CH═C),6.21(1H, s, CH═C), 7.50(5 H, m, Ar—H), 7.72(4 H, m, Ar—H) and 8.22(4 H,m, Ar—H). δ_(c) (63.5 MHz, CDCl₃) 18.4 (CH₃), 65.7 (CH₂), 122.7,123.7(C-oxadiazole), 126.2, 136.0 (C═C), 140.0, 144.6, 127.2, 127.4,127.7, 128.2, 128.4, 129.0 (Ar), 164.3 and 164.6 (oxadiazole), 167.1(C═O); ν_(max) (CHCl₃)/cm⁻¹: 3012(C—H), 1717(CO—O), 1614, 1550, 1483(Ar), 965 oxadiazole). [Found: C, 75.5; H, 4.9; N, 6.9. C₂₅H₂₀N₂O₃requires C, 75.74; H, 5.08; N, 7.07%].

Scheme 7: Synthesis of methacrylate monomer (16)

EXAMPLE 3

The Synthesis of Methacrylate Monomer TPV (16)

Synthesis of the alcohol (15)

To a solution of the bis-phosphonate (11) (3.3 g, 8.73 mmol) in DMF (30ml), cooled to 0° C., was added sodium hydride (1.0 g, 25.0 mmol, 60%dispersion in mineral oil). The reaction mixture was stirred for 15minutes. The substituted benzaldehyde (12) (1.75 g, 9.1 mmol) andterephthalaldehyde mono(diethyl)acetal (12) (2 ml, 10.05 mmol) in DMF(10 ml) was then added from a dropping funnel and the reaction mixturewas then stirred for 2 h at 0° C. in a cooling bath. HCl (3M, 10 ml) wasadded drop-by-drop to the cooled reaction mixture in order to destroyexcess NaH and remove the acetal protecting group. The acidified mixturewas stirred for 2h at room temperature and then poured into a largeexcess of distilled water. The crude mixture of products (yellow solids)were filtered out under suction and dried in vacuo. TLC(CH₂Cl₂)indicated three different compounds in the mixture of products. Thesecompounds were separated by flash column chromatography (CH₂Cl₂). Thedesired aldehyde (14) was obtained (1.11 g, 32.1%).

The aldehyde (14) (1.1 g, 2.78 mmol) was dissolved in THF (30 ml) andcooled to 0° C. LiAlH₄ (0.2 g, 5.0 mmol) was added slowly in twoportions. The mixture was then refluxed overnight at 60° C. Dilute acid(1M, 100 ml) was added, drop-by-drop to the cooled reaction mixture, todestroy excess LiAlH₄ and dissolve the alumina sludge formed. Theaqueous mixture was extracted with CH₂Cl₂ (3×50 ml). The three CH₂Cl₂portions were combined, washed with brine (50 ml), dried with anhydroussodium sulfate and CH₂Cl₂ was evaporated off to yield the crude alcohol(15). The product was purified by flash column chromatography (elutingwith 1:1 CH₂Cl₂-hexane to CH₂Cl₂ v/v) and was obtained as ayellowish-green solid (1.01 g, 2.54 mmol, 91%). [Overall yield: 29.1%];R_(f) 0.53 (CH₂Cl₂); ν_(max) (KBr)/cm⁻¹ 3386 (OH), 1493 (C═C), 1456(C═C), 1362 (Ar), 1248 (C—O); δ_(H) (400 MHz, CDCl₃) 1.34 (9 H, s,t-Bu), 3.87 (3 H, s, OCH₃), 4.70 (2 H, d, J 4.6, CH₂), 6.84 (1 H, d, J8.5, C═CH), 7.05-7.15 (3 H, m, J 9.4 and 6.4, C═CH), 7.27 (1 H, d, J2.5, Ar—H), 7.36 (2 H, d, J 8.1, Ar—H), 7.46-7.55 (7 H, m, Ar—H), 7.59(1 H, d, J 2.5, Ar—H)

Synthesis of Methacrylate Ester (16)

To a solution of alcohol (15) (1.01 g, 2.54 mmol) and triethylamine (0.6ml, 4.3 mmol) in dry CH₂Cl₂ (20 ml), was added methacryloyl chloride(0.4 ml, 4.09 mmol). The mixture was stirred at room temperature for 3h. TLC(CH₂Cl₂) showed no presence of starting material (15). CH₂Cl₂ (80ml) was added to the reaction mixture which was then washed with Na₂CO₂(50 ml), HCl (1M, 50 ml) and brine (50 ml). The aqueous portions wereextracted with a further portion of CH₂Cl₂ (50 ml). The two CH₂Cl₂portions were combined, dried with anhydrous magnesium sulfate andCH₂Cl₂ was evaporated off to yield the crude ester (16). The product waspurified using flash column chromatography (eluting with 1:6CH₂Cl₂-hexane followed by 1:4 CH₂Cl₂-hexane v/v). The ester was obtainedas a green solid which luminescences blue under uv radiation (0.76 g,1.63 mmol, 64.2%). R_(f) 0.13 (1:9 ether-hexane v/v); ν_(max) (KBr)/cm⁻¹1716 (C═O), 1638 (C═C), 1603 (C═C), 1515 (Ar), 1494 (Ar), 1462 (Ar),1156 (C—O); δ_(H) (400 MHz, CDCl₃) 1.34 (9 H, s, t-Bu), 1.97 (3 H, s,CH₃), 3.88 (3 H, s, OCH₃), 5.19 (2 H, s, CH₂), 5.59 (2 H, s, C═CH), 6.16(1 H, s, C═CH), 6.84 (1 H, d, J 8.6, C═CH), 7.05-7.14 (3 H, m, J 11.0and 5.2, C═CH), 7.28 (1 H, d, J 2.4, Ar—H), 7.36 (2 H, d, J 8.1, Ar—H),7.46-7.56 (7 H, m, Ar—H), 7.60 (1 H, d, J 2.4, Ar—H); δ_(c) (100 MHz,CDCl₃) 167.29 (CO₂), 154.94 (C), 143.34 (C), 137.71 (C), 137.44 (C),136.17 (C), 135.34 (C), 128.91 (C), 128.53 (C), 128.40 (C), 127.71 (C),126.89 (C), 126.83 (C), 126.61 (CH), 125.85 (CH), 125.64 (C), 124.19(CH) 123.55 (CH), 110.65 (CH), 66.22 (CO₂CH₂Ar), 55.65 (OCH₃), 34.19(CMe₃), 31.56 (C(CH₃)₃), 18.37 (CH₃)

EXAMPLE 4

The polymerisation of methacrylate PPD monomer by anionic polymerisation(PMA-PPD-1)

Preparation of (2,6-di-tert-butyl-4-methylphenoxy) diisobutylaluminium[Al(BHT)^(i)Bu₂]:

Di-tert-butyl-4-methylphenol (4.412 g, 20.0 mmol) was dissolved intoluene (20 ml). Triisobutyl aluminium (20 ml, 1M in toluene) was addedby syringe, under N₂. The temperature was allowed to rise to 50° C.while butane gas was evolved. The mixture was then stirred at 50° C. for1 h. The flask was sealed with a septum and the mixture used as a stocksolution.

The polymerisation:

n-Butyl lithium (0.05 ml, 15%) and Al(BHT)Bu₂ (1.5 ml) were dissolved intoluene (2 ml) and stirred under nitrogen for 30 mins at 0° C. Asolution of the monomer (14) (0.33 g, 0.9 mmol) in toluene (2 ml) was atfirst slowly added dropwise and a yellow colour formed. The monomer wasthen run in more quickly. After 2 h, the colour had disappeared and thereaction appeared to have stopped. More BuLi (0.05 ml, 15%) was thenadded. After a further 3 h, no polymer was observed by TLC. The reactionwas therefore terminated by adding methanol. CH₂Cl₂ (200 ml) and water(100 ml) were added and the polymer was found at the bottom of theflask. The polymer was then extracted with excess CHCl₃. The solvent wasremoved under reduced pressure and the resulting polymer dissolved inthe minimum amount of CHCl₃, filtered through a sand filled pipette andadded to MeOH(200 ml). The resulting white polymer was collected byfiltration giving polymer (15) (ca. 50 mg), m.p. 190-230° C.;ν_(max)(KBr)/cm⁻¹ 2961, 1734 s (C═O), 1617, 1495, 1138, 1067 and 842;δ_(H) (250 MHz, CDCl₃) 1.24 (12 H, bs, α—CH₃ and C(CH₃)₃ group), 1.77 (2H, b, CH₂), 5.29 (2 H, s, CH₂), 7.37 and 7.88 (2×4H, b, Ar—H); δ_(c)(63.5 MHz, CDCl₃) 31.0 (CH₃ and C(CH₃)₃), 35.0(C(CH₃)₃), 44.9 (CH₂),66.1 (CH₂—OH), 120.8, 123.8, 125.9, 126.6, 126.9, 129 1, 138.4, 155.2,163.6 and 164.5 (Ar) and 176.5 (C═O). [Found: C, 64.6; H, 5.9; N, 6.3;C₂₃H₂₄O₃N₂ requires: C, 73.4; H, 7.4; N, 7.4%]; GPC assay revealed(CHCl₃, polystyrene as standard): M_(n)=36,000, M_(w)=489,000.

EXAMPLE 5

Polymerisation of methacrylate PPD monomer (9a) by radicalpolymerisation (PMA-PPD-2):

Monomer (9a) (0.33 g, 0.89 mmol) was dissolved in AIBN solution inbenzene (5 ml, 0.3 mg, 1.83×10⁻⁶ mol). The ratio of AIBN/monomer is0.21% (mol/mol). After removing ca. 4 ml of benzene in vacuo, thesolution was thoroughly degassed by several freeze-thaw-pump cycles(five to eight times). The reaction mixture was stirred at 80° C. for 2h before cooling down to room temperature. The viscous reaction mixturewas poured into MeOH (10 ml) to obtain a white precipitate which wasthen, washed with MeOH (3×2 ml) and dried to yielded crude polymer (9a)(0.22 g, 69%). The polymer was further purified by dissolving inchloroform and reprecipitation in MeOH (repeated 3 times). δ_(C) (250MHz, CDCl₃) 0.67, 0.98(3H, b, α—CH₃), 1.24(9 H, C(CH₃)₃), 1.87(2H, CH₂),4.87(2H, b, CH₂), 7.37, 7.88(2×4 H, Ar—H); δ_(C) (100 MHz, CDCl₃) 16.9,19.0(a-CH₃), 31.0(C(CH₃)₃), 35.0(CMe₃), 45.0(CH₂), 54.1(CC═O),66.1(CH₂OCO), 120.8, 123.8, 125.9, 126.7, 126.9, 129.1, 138.5,155.2(Ar), 163.7, 164.5(oxadiazole), 176.8(C═O); ν_(max) (CHCl₃)/cm⁻¹:2966(C—H), 1728(C═O), 1615, 1552, 1494(Ar), 964(oxadiazole); [Found: C,72.69; H, 6.30; N, 7.22; C₂₃H₂₄N₂O₃ requires: C, 73.38; H, 6.43; N,7.44%]; GPC assay revealed (CHCl₃, polystyrene as standard)M_(n)=52,000, M_(w)=127,000, M_(w)/M_(n)=2.46.

EXAMPLE 6

The polymerisation of mathacrylate PPD monomer (9a) by radicalpolymerisation method (PMA-PPD-3)

The polymerisation procedure is similar to Example 5 except AIBN wasused as initiator (0.5% by mol with respect to amount of monomer). Afterpurification by dissolving in CHCl₃ followed by precipitation into MeOH(repeated three times), polymer (9a) was obtained(55%). GPC assayrevealed (CHCl₃, polystyrene as standard): M_(n)=34,000, M_(w)=103,000,M_(w)/M_(n)=2.99.

EXAMPLE 7

Polymerisation of methacrylate PBD (9b) (PMA-PBD-1):

The polymerisation of monomer (9b) is similar to that of (9a) in Example5. Thus, monomer (9b) (0.35 g of, 0.885 mmol) was dissolved in a benzenesolution containing AIBN (5.4 ml, 0.73 mg AIBN) (AIBN/monomer=0.5%, bymol). Excess benzene was evaporated of in vacuo until ca. 0.5 ml to 1.0ml of benzene remained in the reaction mixture. The solution was thencompletely degassed using several freeze-thaw-pump cycles (five to eighttimes). The reaction mixture was stirred at 80° C. under a N₂atmosphere, for 2 h. On cooling to room temperature, the viscousreaction mixture was poured into methanol-acetone (20 ml, 1:1 v/v) toobtain a white precipitate. The polymer was then purified by repeatedlydissolving in CHCl₃ and precipitating into methanol-acetone (repeated 3times). After drying in vacuo, (9b) was obtained as a white powderysolid (0.23 g, 66%). δ_(H) (250 MHz, in CDCl₃) 0.66-0.98(3H, b, a-CH₃),1.90(2 H, b, CH₂), 4.86(2H, b, CH₂), 7.28, 7.47(9 H, b, Ar—H), 7.85(4 H,b, Ar—H); δ_(c) (100 MHz, CDCl₃) 18.5(CH₃), 29.5(CH₃), 44.9(CH₂),65.7(CH₂), 122.7, 123.7(Ar-oxadiazole), 126.9, 127.2, 127.4, 127.7,128.1, 128.4, 128.8 and 129.0(Ar), 139.4, 144.5(Ar—Ph, Ar—CH₂O),163.8(C, oxadiazole), 164.2(C, oxadiazole); ν_(max) (KBr)/cm⁻¹: 3010(C—H), 1730 (CO—O), 1614, 1550, 1484(Ar), 964(oxadiazole); [Found: C,74.44; H, 4.92; N, 6.66; C₂₅H₂₀N₂O₃ requires: C, 75.74; H, 5.08; N,7.07%]; GPC assay revealed (CHCl₃, polystyrene as standard)M_(n)=89,000, M_(w)=103,000.

EXAMPLE 8

The polymerisation of mathacrylate monomer PBD (9b) (PMA-PBD-2):

The polymerisation procedure is similar to Example 7 exceptchlorobenzene rather than benzene, was used as solvent. The polymer wasthen purified by repeatedly dissolving in CHCl₃ and precipitating intomethanol-acetone (repeated three times). (9b) was obtained in 50% yield.GPC assay revealed (CHCl₃, polystyrene as standard): M_(n)=4,080,M_(w)=42,500.

EXAMPLE 9

The polymerisation of methacrylate TPV (16) (PMA-TPV):

The polymerisation of monomer (16) is quite similar to that of monomer(9). Thus, monomer (16) (0.205 g, 0.44 mmol) was dissolved in benzenesolution (2.5 ml) containing 0.35 mg of AIBN (10.8 mg, 0.85 mmol). Thesolution was then concentrated by evaporating off some benzene in vacuoand then thoroughly degassed by using the freeze-thaw-pump method(repeated five times). The reaction mixture was then stirred at 80° C.for 2 h under an inert nitrogen atmosphere. The homopolymer wasprecipitated out in excess methanol and purified by dissolving in CHCl₃and reprecipitation in excess MeOH (repeated twice). The polymer wasdried overnight in vacuo and was obtained as a pale yellow powdery solid(0.11 g, 54%). ν_(max) (KBr)/cm⁻¹ 1720 (C═O), 1613 (C═C), 1514 (Ar),1465 (Ar), 1150 (C—O); δ_(H) (400 MHz, CDCl₃) 0.5-1.1(b, backbone α-Me),1.1-1.25 (b, backbone CH₂), 1.29 (9 H, s, C(CH₃)₃), 3.74 (3 H, s, OCH₃),4.65-5.2 (2 H, b, CO₂CH₂), 6.7-7.1 (2 H, b, CH═CH), 7.1-7.7 (13 H, b,CH═CH and Ar—H); l_(max)/nm (CHCl₃): 245, 324; GPC assay revealed(CHCl₃, polystyrene as standard) M_(n)=161,000, Mw=702,000,M_(w)/M_(n)=4.37.

EXAMPLE 10

‘Screened’ anionic polymerisation of methyl methacrylate of methacrylatemonomer TPV (16) by anionic polymerisation

10.1 Preparation of 2,6-di-tert-butyl-4-methylphenoxy)diisobutylaluminium (Al(BHT)^(i)Bu₂1

Di-tert-butyl-4-methylphenol (4.412 g, 20.0 mmol) was dissolved intoluene (20 ml). Triisobutyl aluminium (20 ml, 1M in toluene) was addedby syringe, under N₂. The temperature was allowed to rise to 50° C.Butane gas was evolved. The mixture was then stirred at 50° C. for 1 h.The flask was sealed with a septum and the mixture was used as a stocksolution.

10.2. Polymerisation of methyl methacrylate

A solution of Al(BHT)^(i)Bu₂ (3 ml, 1.5 mmol, 0.5M in toluene) was mixedwith toluene (15 ml) in a 3 neck 100 ml RB flask fitted with a pressureequalising dropping funnel, N₂ balloon and a spetum. tert-Butyllithium(0.3 ml, 1.7M in pentane) was then added by syringe, with stirring.Several minutes were allowed to elapse to permit complete complexationof the two metal alkyls. Methyl methacrylate (MMA) (2 ml, 1.87 g, 18.7mmol) was added drop-by-drop from the dropping funnel. The mixture wasstirred at 0° C. for 1 h. The addition of MMA produced a pronouncedyellow colour in the solution but on completion of the polymerisation,the solution is colourless. The polymer was precipitated out in excesshexane and dried in vacuo overnight. Yield (1.7 g, 90%); m.p. 173-280°C.; ν_(max) (KBr)/cm⁻¹ (1731 (C═O), 1150 (C—O); δ_(H) (400 MH\, CDCl₃)0.75-1.1 (b, 3H, α-CH₃), 1.7-2.1 (b, 2H, CH₂), 3.59 (s, 3H, CH₃);Tactility δ_(H) (triad, %); 0.83 (rr, 68.8%), 1.01 (mr, 31.2%). GPC inchloroform revealed M_(n) 25,980, M_(w)/M_(n)=1.35.

EXAMPLE 11

The copolymerisation of methacrylate PBD and TPV:

The copolymerisation of monomer (9b) and monomer (16) was been carriedout using radical copolymerisation method that is similar tohomopolymerisation. Thus, monomer (9b) (0.211 g., 0.532 mmol) and (16)(0.250 g, 0.537 mmol) were first dissolved in a benzene solution (6.5ml) that contain 0.8839 mg of AIBN (AIBN/(17+18)=0.5%, by mol) to form ahomogeneously dispersed solution. The solution was then concentrated toca. 1 ml by evaporating off some benzene in vacuo and then, completelydegassed by using the freeze-thaw-pump method (repeated five times). Thereaction mixture was stirred at 80° C. for 2 h under an inert nitrogenatmosphere. After cooling down to room temperature, the viscous solutionwas poured into MeOH(20 ml) to obtain a white precipitate which was thenfurther purified by repeatedly dissolving in chloroform andprecipitating into methanol (repeated three times). The copolymer wasobtained as a light yellow powdery solid(0.29 g, 63%). δ_(H) (250 MHz,CDCl₃) 0.67-1.16(2×3H, b, 2×a-CH₃), 1.33(9 H, s, ^(t)Bu), 1.61(4 H,CH₂), 3.88(3 H, OCH₃), 4.82(4 H, s, CH₂), 6.72-7.9(24 H, b, Ar—H);δ_(C)(100 MHz, CDCl₃) 31.5(C(CH₃)₃), 34.1(CMe₃), 55.5(OCH₃),110.5(CH═CH), 123.4, 124.0, 126.6, 127.0, 127.2, 127.4, 127.8, 128.2,128.5, 129.0, 137.4(Ar); ν_(max)(KBr)/cm⁻¹ 2949(C—H), 1724 (C═O), 1610,1548(Ar), 961(oxadiazole); GPC assay revealed (CHCl₃, polystyrene asstandard) M_(n)=44,000, Mw=242,000, M_(w)/M_(n)5.45.

EXAMPLE 12

Poly(methacrylate) PPD as single electron transporting layer

In order to evaluate the applicability of the polymers in LED devices,two double layered LED devices have been fabricated using PPV as a holetransport layer and either aluminium or calcium as the negativeelectrode.

LED device fabrication:

ITO glass was cleaned in an ultrasonic bath with detergent solution for20 minutes and then rinsed with distilled water, acetone and isopropanolbefore drying in a stream of N₂. The dry and absolutely clean ITO glasssubstrate was then spin-coated with a PPV precursor solution (1% inmethanol) at room temperature at 2000 rpm for 20 minutes. Thermalconversion of the PPV precursor was carried out at 280° C. in vacuo (ca.0.1 mmHg) for 4 h to obtain a PPV layer (with thickness of ca. 40 nm).The PPV layer functions as both a hole-transport and light-emittinglayer. The oxadiazole containing polymer PMA-PPD-2 (usually 2% inchloroform) was then spin-coated onto the converted PPV layer beforedepositing aluminium on the top to form the double layer LED device. Theelectrodes were led out using a copper adhesive tape strip and thencovered with PVC adhesive tape to prevent contact with air.

(1) ITO/PPV/PMA-PPD/Al No light emission below 28V

(2) ITO/PPV/PMA-PPD/Ca Green yellow light emission

The above results show that when aluminium is used as the negativeelectrode, incorporation of a PMA-PPD layer in the double layer devicehas no apparent benefits. However, light emission(below 28V) is enhancedwhen calcium is used as the cathode. FIG. 1 shows that the internalquantum efficiency of the double layer device(2) can be increased byabout four folds, while the turn-on voltage is apparently reduced (FIG.2).

EXAMPLE 13

Poly(methacrylate) (PPD) used as an electron transporting layer in theform of a blend, with stilbene containing poly(methacrylate) derivative(TPV):

Alternatively, PMA-PPD has been used in a blend with a bluelight-emitting polymer (PMA-TPV), with PPV being used as a holetransporting layer, in a series of devices. These devices werefabricated using the similar procedure described in Example 12, exceptPMA-TPV(2% in chloroform), and a blend solution of PMA-TPV andPMA-PPD-2(1:1 w/w in chloroform) were used instead.

(3) ITO/PMA-TPV/Ca No light emission

(4) ITO/PPV/PMA-TPV/Ca No light emission

(3) ITO/PPV/Blend of PNA-TPV+PMA-PPD/Ca Blue light emission and gradulachenge to green light emission

(6) ITO/PPV/PMA-TPV+PMA-PPD/Al No light emission

These results suggest that PMA-TPV does not electroluminese bellow 28Vunless an electron transporting polymer PMA-PPD is also used (device 3).For device 4, blue light emission was initially observed but the colourgradually changed to green within 20 minutes on continuous chargeapplication at a bias voltage of ca. 15V (as shown in FIG. 3). FIG. 4bshows that the internal quantum efficiency of the device increased afterstoring the device for a week.

EXAMPLE 14

Poly(methacrylate) PBD as a single electron transport layer:

According to the LED fabrication procedure described in Example 12,PMA-PBD-1 solution in chloroform was spin-coated onto a PPV layer, on anITO glass substrate, thus forming a LED device using PMA-PBD as theelectron transporting layer:

(7) ITO/PPV/PMA-PBD/Ca. Green light emission

Green light emission was observed when a bias voltage of 15V wasapplied.

EXAMPLE 15

Poly(methacrylate) PBD used as electron transport layer in the form of ablend with poly(methacrylate) TPV as the emitting polymer:

A blend solution of PMA-PBD-1/PMA-TPV(1:1 w/w) in chloroform was used tospin-coat a film onto a layer of PPV, on an ITO glass substrate.

(8) ITO/PPV/PMA-PBD+PMS-TPV/Ca Blue light emission

Blue light emission was observed at a bias voltage of 20V in the first30 minutes followed by a continuous green light emission (FIG. 5). ThePMA-PBD polymer is used as an electron-transporting functional layer,while the PMA-TPV polymer was used to produce blue light emission. ThePMA-TPV polymer also exhibits some cross-linking potential.

EXAMPLE 16

Poly(methacrylate) PBD-TPV copolymer used as a blue light emittinglayer, in a double layer device:

In an series of LED devices, it has been found that incorporation ofPMA-PBD showed no benefit in enhancing light-emission from a PPV orPMA-TPV layer, when aluminium was used as the cathode [devices (9) and(10)]. However, PBD segments in the copolymer PMA-TPV-PBD does enhanceor aid blue light emission from the TPV chromophores in the copolymer[as shown in device (13)].

(9) ITO/PPV/Al No light emission

(10) ITO/PPV/PMA-PBD/Al No light emission

(11) ITO/PPV/PMA-TPV/Al No light emission

(12) ITO/PPV/Blend of PMA-TPV+PMA-PBD/Al Blue light emission but lessstable

(13) ITO/PPV/Copolymer of PMA-TPV-PBD/Al Blue light emission

These results suggest that the use of electron transporting segments inthe copolymer is better than that in the form of a blend [compare device(12) with (13) and (14)]. FIG. 6 shows that the turn-on voltage for thedevice is about 16V, and the light intensity will increase along withthe increase of the applied voltage until 23V (device break-down occursbeyond that voltage) (FIG. 6). It can be seen from FIG. 7, that thecolour of the light emitted is blue since the peak maxima in theelectroluminescence spectrum is located at 457 nm. This is in the blueregion of the visible spectrum. It can also be seen from FIG. 8 (line2), that there is light emission from the PPV layer since there are twoelectroluminescent shoulders at 554 nm and 507 nm, which are typical ofPPV emission [FIG. 8 (line 3)]. The PPV emission is further confirmedwhen the colour of light emitted gradually changes from blue to green oncontinuous charge application. This suggest the break-down of the TPVchromophores in the PMA-TPV-PBD copolymer, thus leaving PPV as the solelight-emitting polymer. FIG. 9 shows that the device has a fairly highinternal quantum efficiency (with 0.035%) considering aluminium is usedas the cathode.

EXAMPLE 17

Copolymer PMA-TPV-PBD used as a blue light emitting layer in a singlelayer device:

The copolymer solution (2% in chloroform) was directly spin-coated ontoa clean ITO glass substrate followed by the deposition of aluminium toform a single layer LED device:

(14) ITO/PMA-TPV-PBD/Al Blue light emission

Blue light emission was observed when a bias voltage (20V) was appliedbut the device appears to be less stable compared to the double layeredLED device (13).

THE PREPARATION AND APPLICATION OF MAIN CHAIN LED POLYMERS THROUGH APRECURSOR ROUTE

Poly(methacrylates) have many advantages such as high transparency, highresistance to chemicals and good mechanical strength. High molecularweight poly(methacrylates) as well as multi-functional copolymers canalso be easily obtained. However, poly(methacrylate) derivatives may notbe good candidates for polymers which exhibit high stability andresistance to an electrical field. Therefore, they may have a life-timeproblem in applications involving LED devices. In order to prevent thisproblem, one approach involves the introduction of another chain segmentwhich contains cross-linkable groups such as TPV. Another way to improvethe resistance to an electrical field is to choose other types ofpolymer chains such as rigid-rod polymers or ladder polymers. However,there is a severe processability problem for rigid-rod or ladderpolymers due to their low solubility in conventional organic solvents.The processability of these polymers can be improved by using a solubleprecursor which can be converted to a rigid and conjugated polymer.Here, we have tried a precursor route for the synthesis of polyaromaticoxadiazoles as shown in Scheme 8 and Scheme 9.

Scheme 8: Precursor route for the synthesis of an aromatic oxadiazolepolymer

Scheme 9: A precursor route for the synthesis of a ^(t)Bu-aromaticoxadiazole polymer

EXAMPLE 18

Synthesis of Polyaromatic hydrazide (24):

1,3-isophthaloyl dichloride (5.31 g, 26.17 mmol) was added to the slurryof (23) (5.08 g, 26.17 mmol) in N-methylpyrolidone(NMP) (50 ml) and LiCl(4.86 g) in a 250 ml, 3-neck RB flask. The reaction was stirred for 5 hat 0° C. before pouring the viscous reaction mixture into water toobtain a white precipitate which was then washed with 1% LiOH(aq)solution, water and methanol respectively. The polymer was purified bySoxhlet extraction using methanol (8 h) and dried in vacuo at 110° C.for 8 h. (24) was obtained as a white powdery solid(7.82 g, 92%). δ_(H)(200 MHz, DMSO-d₆) 7.73(1H, s), 8.15(2 H, d, Ar—H), 8.09(4 H, s), 8.52(1H, s, Ar—H), 10.77(4H, s, 2×NHNH); δ_(c) (100 MHz, DMSO-d₆) 127.2,128.5, 130.0, 131.4, 133.0, 135.5(Ar), 165.3C═O), 165.5(C═O);ν_(max)(KBr)/cm⁻¹ 3252(N—H), 1685(C═O), 1654(CO—NH), 1560, 1508, 1488(Ar); Intrinsic visicosity: 0.5 dL/g (30° C. in DMSO).

EXAMPLE 19

Preparation of polyaromatic oxadiazole (25):

The polyaromatic hydrazide (24) will be thermally converted to (25) at270° C. (or above) under nitrogen or in vacuo for at least 24 h.ν_(max)(KBr)/cm⁻¹: 1700(residue of CO—NH), 1609, 1543, 1478, 1458(Ar),961(Oxadiazole); λ_(max/film): 227, 335 nm.

EXAMPLE 20

Preparation of polyaromatic hydrazide-tert-Bu (27):

A 250 ml 3-neck RB flask with a condensor, a mechanic stirrer andthermometer was charged with (23) (3.88 g, 0.02 mol),5-tert-butyl-1,3-isophthalic acid (26) (4.44 g, 0.02 mol), and LiCl (6.0g) dissolved in dry NMP (60 ml) and dry pyridine (40 ml). The reactionwas carried out in the presence of diphenyl phosphite (14.05 g, 60 mmol)at 120° C. for 2.5 h. The sticky, opaque solution was poured intomethanol(500 ml) to obtain a white precipitate which was then washedwith methanol (4×200 ml) and then, extracted using methanol in a Soxhletapparatus for 20 h. After drying in vacuo, (27) was obtained as a whitesolid (5.85 g, 77%). δ_(H) (200 MHz, DMSO-d₆) 1.43(9H, s, C(CH₃)₃),8.10(4H, b), 8.20(2 H, b), 8.37(1H, Ar—H), 10.77, 10.80(4H, s, 2×NHNH);σ_(c) (100 MHz, DMSO-d₆) 31.0(C(CH₃)₃), 35.1(CMe₃), 122.1, 124.8, 127.9,132.9, 135.6, 151.8(Ar), 165.3(C═O), 165.7(C═O); ν_(max)(KBr)/cm⁻¹3252(CO—N—H), 2957(C—H), 1654(CO—NH), 1543, 1478(Ar); [Found: C, 60.60;H, 5.64; N, 14.47. C₂₀H₂₀N₄O₄ requires: C, 63.13; H, 5.30; N, 14.47%].

EXAMPLE 21

Preparation of polyaromatic oxadiazole-tert-Bu (28):

The polyaromatic hydrazide-^(t)Bu polymer (27) was thermally convertedinto polymer (28) under nitrogen or in vacuo at 270° C. (or above) forat least 24h. v_(max)(KBr)/cm⁻¹ 2957 (C—H), 1543 s, 1482 (Ar), 962 )oxadiazole); [Found: C, 68.64; H, 4.65; N, 15.64. C₂₀H₁₆N₄O₂ requires:C, 68.54; H, 4.69; N, 16.28%].

THE PREPARATION AND APPLICATION OF MAIN CHAIN POLYMERS THROUGH THEINTRODUCTION OF FLEXIBLE SPACERS

The introduction of a flexible spacer into a conjugated or rigid polymerchain will usually enhance the solubility of the polymer. The followingexamples illustrate the preparation and application of three differentpolymers with a hexafluopropylene spacer. (Scheme 10)

EXAMPLE 22

Preparation ofPoly(phenylene-1,3,4-oxadiazole-2,5-diylphenylene-2,2-hexafluoropropylidene)(31):

Phosphorous pentoxide (2.95 g, 20.0 mmol) was dissolved inmethanesulfonic acid (20 ml) upon stirring at 80° C. over 30 min.Hydrazine sulfate (1.302 g, 10.0 mmol) and2,2-bis(4-carboxyphenyl)hexafluoropropane (29) (3.923 g, 10.0 mmol) wereadded and the mixture stirred for 24 h at 80° C. The solids dissolvedslowly within 30 min. On cooling to room temperature, the yellow viscoussolution was poured into water (300 ml) and neutralised with saturatedaqueous Na₂CO₃ (40 ml). The precipitate (fibre-like) was filtered outunder suction and washed with water (3×300 ml), and finally purified bydissolving in chloroform and precipitating out in methanol (repeatedthree times). (31) was obtained as grey-white fibres whichmelted/decomposed above 270° C. (2.79 g, 75.4%). λ_(max) (chloroform)300 nm; λ_(max) (solid film) 290 nm; ν_(max) (KBr)/cm⁻¹ 1618, 1585,1551, 1499, 1420, 1256, 1210, 1175, 1140, 1071 10120, 971, 928, 840 723;δ_(H) (400 MHz), CDCl₃) 7.60-8.18 (8H, b, Ar-H); δ_(C) (100 MHz, CDCl₃)122.3, 124.8, 125.3 (ipso-C), 127.1 and 131.0 (CH), 136.5 (ipso-C);[Found: C, 54.99; H, 2.29; N, 7.56. C₁₇H₈F₆N₂O requires: C, 55.15; H,2.18; N, 7.57%]; The polymer was insoluble in ethyl acetate, ether,acetonitrile, toluene and acetone but soluble in tetrahydrofuran,dichloromethane and chloroform. GPC assay revealed (CHCl₃, polystyreneas standard, 10 ml/min flow rate) M_(n)=11,800, Mw=143,000,M_(w)/M_(n)=12.

Scheme 10: The synthesis of fluorine-containing polyaromatic oxadiazoles

EXAMPLE 23

The preparation of polymer (32):

The synthesis procedure for polymer (32) is quite similar to that ofpolymer (31). Phosphorus pentoxide (2.70 g) was dissolved inmethanesulfonic acid (16.0 ml) upon stirring at 80° C. over 30 min.Hydrazide (23) (1.6355 g, 8.42 mmol) and 2,2-bis(4-carboxyphenyl)hexafluoropropane (29) (3.301 g, 8.42 mmol) were added and the mixturestirred for 24 h at 80° C. After the mixture was cooled to roomtemperature, the yellow viscous solution was poured into water (300 ml)and neutralised with saturated aqueous Na₂CO₃ (40 ml). The precipitatewas filtered out under suction and washed with water (3×300 ml), andfinally purified by Soxhlet extraction with methanol for 48 h. (32) wasobtained as a grey powdery solid which melted/decomposed above 270° C.(3.43 g, 79.2%). λ_(max) (solid film) 312 nm. ν_(max) (KBr)/cm⁻¹ 1725,1617, 1576, 1552, 1497, 1415, 1327, 1256, 1210, 1174, 1140, 1072, 1017s,970, 928, 838, 722; δ_(H) (400 MHz, CDCl₃) 7.43 (4H, s, Ar-H), 7.64 (4H,s, Ar-H), 7.85 (4H, s, Ar-H); δ_(C) (100 MHz, CDCl₃) 123.8, 124.3,127.2, 127.8, 129.8, 130.8, 133.0, 133.8, 141.6.

EXAMPLE 24

The preparation of polymer (33)

The synthesis procedure of polymer (33) is quite similar to that ofpolymer (31). Phosphorus pentoxide (1.860 g) was dissolved inmethanesulfonic acid (12.0 ml) upon stirring at 80° C. over 30 min.Hydrazide (23) (0.611 g, 3.148 mmol), hydrazine sulfate (0.410 g, 3.148mmol) and 2,2-bis(4-carboxyphenyl)hexafluoropropane (29) (2.47 g, 6.30mmol) were added and the mixture stirred for 24 h at 80° C. After themixture had cooled down to room temperature, the yellow viscous solutionwas poured into water (300 ml) and neutralised with saturated aqueousNa₂CO₃ (40 ml). The precipitate was collected by suction filtration andwashed with water (3×300 ml), and finally purified by Soxhlet extractionwith methanol for 48 h. (33) was obtained as a grey powdery solid whichmelted/decomposed about 270° C. (2.54 g, 91.4%). λ_(max) (solid film)320 nm. δ_(H) (250 MHz, CDCl₃) 7.41 (4H, s, Ar-H), 7.90 (4H, s, Ar-H),8.13 (2H, s, Ar-H); δ_(C) (100 MHz, CDCl₃) 124.2, 124.4, 125.0, 127.8,128.5(C), 130.4, 131.5, 134.5(CH), 142.3(C).

EXAMPLE 25

Polymer (31) as a single electron transport layer

Clear polymer (31) solution (1% in chloroform, filtrated through 0.45 μlmembrane) was spin-coated onto a PPV layer (ca. 40 nm thickness on anITO glass substrate). Aluminium was then evaporated on top of the filmof polymer (31) (ca. 40 nm) to form a double layer polymer LED device[ITO/PPV/P−31/Al]. A more stable green light emission was obtained at abias voltage of 22 V, in comparison to a device without P−31.

EXAMPLE 26

Polymer (31) as electron transporting polymer in a blend form withpolyalkylthiophene

A clear blend of polymer solution (1% in chloroform, filtrated through0.45 ul membrane) [1:1 ratio of polymer-(31):poly[3-(2-dimethyl ethyl)thiophene)] was spin-coated onto a dry and clean ITO glass substrate.Aluminium was then evaporated on top of the film of polymer blend (ca.40 nm) to form a double layer polymer LED device: [ITO/PAT+P−31/Al]. Amore stable yellow light emission was obtained at a bias voltage of 18V, in comparison to a device without P−31.

EXAMPLE 27

Polymer (32) as both an electron transporting polymer andelectroluminescent polymer in a double layer device

A clear solution of polymer (32) (1% in trifluoroacetic acid, filteredthrough 0.6 ul pore size membrane) was spin-coated onto a PPV layer (ca.40 nm thickness on an ITO glass substrate). Aluminium was thenevaporated on top of the film of polymer (32) (ca. 40 nm) to form adouble layer polymer LED device: [ITO/PPV/P−32/Al]. Green light emissionwas observed at a bias voltage of 15 V, which then turned to blue purplewhen a higher bias voltage (28 V) was applied.

The Synthesis of Polythiophenes 45a-c

The synthesis of the relevant polythiophenes 45a-c is shown in Scheme 11

The relevant thiophene monomers 1 and 2 have been reported (K. A.Murray, S. C. Moratti, D. R. Baigent, N. C. Greenham, K. Pichler, A. B.Holmes and R. H. Friend, Synth. Met., 1995, 69, 395-396).

The regioregular polythiophenes chosen to illustrate crosslinkablepolymers are poly(3-hexylthiophene)s containing a small about of11-hydroxyundecyl side chains. The monomers have been copolymerised inratios of 19:1 1:2 up to 2:1 1:2, to give the tetrahydropyranyl acetalprotected copolymers 43. These can be deprotected to give thealcohol-functionalised copolymers 44 (scheme 11). Conversion to theazide is achieved in one step using excess diphenylphosphoryl azide andhas been carried out on 19:1, 9:1 and 4:1 ratio copolymers 44 to giveazidated copolymers 45a, 45b and 45c respectively; no residual alcoholcan be seen by ¹H NMR.

Thermal decomposition of the azide was achieved by heating films ofcopolymers 45a-c to 200° C. under vacuum for 30 minutes; differentialscanning calorimetry of polymer 45b indicates that azide decompositionoccurs above 185° C. Azide decomposition results in loss of nitrogen andthe formation of a highly reactive nitrene which is expected to reactfairly indiscriminately with single and double bonds. A change in theUV-visible absorption spectra of the polymers is observed oncrosslinking; the spectrum shifts to lower wavelength (higher energy)possibly due to a shorter conjugation length due to nitrene insertionalong the polymer backbone and this effect increases with the azidecontent of the polymer (FIG. 11, Table 1). The resulting films werewashed with chloroform and were insoluble but showed a slight colourchange (Table 1). A small amount of soluble, non-crosslinked polymer waswashed from the 19:1 copolymer (ex 45a) but the remaining polymer wasfully insoluble.

TABLE 1 Thermal crosslinking of regioregular polythiophenes withdifferent azide contents. Ratio λ_(max)/nm λ_(max)/nm λ_(max)/nmλ_(max)/nm hexyl: before after CHCl₃ in Polymer azide heat heat washedchloroform 45a 19:1  520 510 502 458 45b 9:1 522 496 488 458 45c 4:1 522486 482 462

The resultant insoluble polythiophene films can be used in deviceformation, as further layers might be spun from solution on top of thepolythiophene without causing any damage. It is also possible thatphysical properties could be tailored by altering the azideconcentration and controlling the conjugation length in the polymer.

Polythiophene device embodiment:

A film of the non-cross linked polythiophene was spun (1000 rpm/40 sec)on a ITO coated glass substrate producing a dark red uniform film. Thesubstrate is baked at 200° C. for 60 minutes in vacuum (5 10⁻⁶ mbar).After cooling the film was carefully washed with chloroform and dried innitrogen. 1000 A of aluminium is evaporated onto the polymer to form thetop contact. Finally the device was encapsulated with an epoxy/glasscombination. FIG. 16 shows a typical IV and LI curve. 2 cd/sqm emissionwas observed at about 100 mA/sqcm with 10 V drive. The emission is redand the emission spectrum is shown in FIG. 17.

In a further embodiment of this invention the UV/VIS properties of thecrosslinked polymers are retained and show response to the solventenvironment without dissolving significantly. The solid films of thecrosslinked polymers are all red, but are orange in contact withchloroform or other good solvents (toluene, THF), indicating solvationof the polymers. The absorption spectra for the 9:1 copolymer (45b) areshown (FIG. 11). This property serves the function of allowing thesepolymer films to be used in detection and sensing devices on account oftheir change in optical properties. Changes in chiroptical propertiescould also be detected in crosslinked polythiophenes carrying chirallymodified side chains. In this way, optical devices can be made whichwould function as sensors or chiral thin film affinity surfaces fordetection of various substrates, such as enantiomers, peptides, proteinsand enzymes.

Crosslinked cinnamate ester derivatives

Poly(methacrylate) polymers 49 (Scheme 12) carrying statisticaloxadiazole side chains, with distyrylbenzene and cinnamate side chainshave been cross linked by photochemical irradiation. The resultingpolymer in a light emitting device emits light blue light efficiently.

Poly(methacrylates) have many advantages such as high transparency, highresistance to chemicals, and good mechanical strength. It is alsorelatively easy to synthesise high molecular weight polymers as well asmulti-functional copolymers. A range of aromatic oxadiazole bondedpolymers, distyrylbenzene bonded polymers, and the copolymers bondedwith both oxadiazole and distyrylbenzene have been synthesised and usedfor electron transporting layer or light emitting layer. However, thedevice of these polymers tend not to be very stable while working,presumably due to the flexible backbone and easy dimerisation betweendifferent distyrylbenzene. In order to overcome this problem, anotherfunctional unit that is UV-photosensitivity crosslinkable, has beencopolymerised to achieve polymethacrylate with electron transportingunit, blue light emitting unit and UV-crosslinkable unit. Better devicestability will be expected as the result of cross linking and thereforesuppress polymer chain movement and dimerisation.

The UV-sensitive 2-(cinnamoyloxy) ethyl methacrylate 47 was synthesisedaccording to the literature [M. Kato, T. Hirayama, Macromol. Rapid.Commun., 1994, 15, 741]. Monomer 47 can be readily polymerised in theinitiating of AIBN. It was found when benzene is sued as solvent, largemajority of the formed polymer is insoluble in common organic solvent,indicating the cross link reaction has been simultaneously resultedduring polymerisation. When the polymerisation is carried out in THF,fully soluble polymer can be obtained at 60° C. for 8 hours. The solventTHF obviously not only plays a solubilising role, but also controls thereactivity of radical species.

The copolymerisation of the aromatic oxadiazole unit 46, distyrylbenzeneunit 48 and the monomer 47 was carried out under a similar conditionsfor the homopolymer. The ratio among the monomers can be varied. Forconvenience, equal weights of the monomers have been used for thecopolymerisation that corresponds to p=0.53, q=0.28 and r=0.19 (Scheme12). Yellow powdery copolymer 49 can be obtained in good yield afterpurification (precipitate twice in methanol). The copolymer 49 issoluble in chlorinated solvents, THF and toluene but insoluble inhexane, methanol. GPC analysis revealed that the molar mass of 49 is11,200/53,500(M_(n)M_(w)). Free standing polymer film can be easilyobtained by casting technique. The polymer has good stability if it iskept in the refrigerator at <0° C.

The polymer 49 fluoresces greenish blue under UV light.

The photocrosslinking behaviour of the copolymer 49

The three unit copolymer contains not only a luminophore and an electrontransporting chromophore, but also a UV-sensitive cross linking unit. Inorder to understand the photocrosslinking behaviour of the polymer, athin film of the polymer was exposed in UV-light for various time. Itcan be seen from FIG. 14 that the copolymer exhibits 3 absorption peaksin the solid state at 200 nm, 295 nm and 400 nm. With increasingexposure time, the intensity of these 3 peaks decreased. The peaks at295 nm and 200 nm are related to the cinnamoyloxy group which will bedecreased as the result of cross linking. The effect on the IRabsorption of the cinnamoyl ester carboxyl group is seen in Table 2.When a film polymer 49 (on a glass plate) was exposed for 5 minutes, thefilm became insoluble in chloroform but still fluoresced blue.Therefore, 5-10 minutes exposure time was appropriate for obtaining across linked and insoluble polymer. The PL spectrum of the resultingcross-linked polymer film showed little change upon further irradiationand maintained constant luminescence efficiency (39%).

TABLE 2 The change of ester group infrared absorption with UV exposuretime Time/ m 0 1 6 16 26 40 60 80 110 IR 1722 1722 1723 1724 1725 17271728 1729 1729 peak (cm- 1)

LED application

Two LED devices have been fabricated using PPV as hole transportinglayer and copolymer 49 with and without UV irradiation (5 minutes) asemissive layer:

A) ITO/PPV/Polymer 49/Al: Pale blue emission (20 V/0.8 mA)

B) ITO/PPV/Polymer 49 irradiated/Al: Pale blue emission (28 V/0.8 mA)

The above results show that polymer 49 can be successfully used as ablue light emitting polymer using stable aluminium as cathode. Moreover,the spin-coated emissive polymer can be easily cured by UV irradiationto become insoluble which leads to crosslinked polymer and results in amore stable polymer LED.

A single layer light emitting device using the polymer 49 as an emissivelayer and calcium as cathode has also been made. Blue light emission hasbeen observed with 0.1% internal quantum efficiency. For a single layerdevice, the quantum efficiency is relatively high. Theelectroluminescence spectrum of the single layer device using polymer 49is shown in FIG. 15.

REPRESENTATIVE SYNTHESIS OF POLYMER 45b

Regioregular 9:1Poly{3-hexyl-co-3-(11-[2-tetrahydropyranyloxy]undecyl)-thi ophene} (43b)

Following the above procedure (for polymer 43a) a mixture of2-bromo-3-hexylthiophene (41) (1.47 g, 5.95 mmol) and2-bromo-2-bromo-3-(5-[2-tetrahydropyranyloxy]undecyl)-thiophene (42)(0.28 g, 0.67 mmol) was polymerised (with one addition of NiCl₂ (dppp)catalyst) to give copolymer 43b (108 mg; 9%) as a deep purple solidfilm. λ_(max) (CHCl₃/nm) 450; δ_(H) (200 MHz, CDCl₃) 0.91 (t, J 6.4,6′-H [3H] of hexyl), 120-1.80 (br m, side-chain Ch₂), 2.81 (2H, br t, J7.6, 1′-H), 3.31-3.54 (0.2H, m, 11′, 6″-H [2H] of 11-THPO-undecyl),3.66-3.90 (0.2H, m, 11′, 6″-H [2H] of 11-THPO-undecyl) 4.57 (0.1H, m,2″-H [1H] of 11-THPO-undecyl) and 6.98 (1H, s, 4-H); GPC (CHCl₃, 450nm)/Da M_(n) 9,5000, M_(w)13,400, polydispersity 1.42.

Regioregular 9:1 Poly {3-hexyl-co-3-(11-hydroxyundecyl) thiophene} (44b)

Following the above procedure (for polymer 44a), regioregular 9:1 poly{3-hexyl-co-(11-[2-tetrahydropyranyloxy]undecyl) thiophene} (43b) (117mg) was treated with methanol/dilute aqueous HCl to give deprotectedcopolymer 44b (104 mg, 93%) as a deep purple solid film. λ_(max)(solid/nm) 526, 550 sh, 600 sh, (CHCl₃/nm) 450; δ_(H) (200 MHz, CDCl₃)0.91 (br t, J −6.4, 6′-H [3H] of hexyl), 1.20-1.80 (br m, side-chainCH₂), 2.81 (2H, br t, J −7.5, 1′-H), 3.62 (0.2H, t, J 6.5, 11′-H [2H] of11-hydroxy-undecyl) and 6.09 (1H, s, 4-H); GPC (CHCl₃, 450 nm)/Da M_(n)11,500, M_(w) 17,000, polydispersity 1.65.

Regioregular 9:1 Poly {3-hexyl-co-3-(11-azidoundecyl)thiophene} (45b)

Following the above procedure (for polymer 45a), regioregular 9:1poly{3-hexyl-co-3-(11-hydroxyundecyl)thiophene} (44b) (77 mg) wasazidated to give copolymer 45b (63 mg, 81%) as a deep purple solid film.λ_(max) (KBr disc)/cm⁻¹ includes 2095 w (azide); λ_(max) (solid/nm) 522,550 sh, 600 sh, (CHCl₃/nm) 450; δ_(H) (200 MHz, CDCl₃) 0.91 (br t, J−6.7, 6′-H [3H] of hexyl), 1.20-1.80 (br m, side-chain CH₂), 2.81 (2H,br t, J −7.4, 1′-H), 3.23 (0.2H, t, J −7, 11′-H [2H] of 11-azidoundecyl)and 6.98 (1H, s, 4-H); GPC (CHCl₃, 450 nm)/Da M_(n) 5,100, M_(w) 11,800,polydispersity 2.34; DSC: exotherm at 185° C., max. at 200° C. (not seenon second sweep—nitrene formation); TGA (%/° C.) 99.5/185, 95.5/270,55/480, <10/600 (N₂ loss=1.6%).

Scheme 11

Scheme 12

What is claimed is:
 1. A polymer capable of electron transport in anoptical device, which polymer comprises a film-forming polymer which issolvent processible or formed from a processible precursor polymer andwhich includes an electron transport segment in the polymer main chainor covalently linked thereto in an electron transport side chain,wherein the electron transport segment comprises the moiety Ar₁-Het-Ar₂in which Ar₁ and Ar₂ are the same as or different from one another andare each selected from aromatic and heteroaromatic units, fused aromaticderivatives thereof and double bonds, and Het is a heteroaromatic ring,wherein the electronic structure of the heteroaromatic ring favourselectron transport.
 2. A polymer according to claim 1, wherein Hetcomprises an electron deficient heteroaromatic group.
 3. A polymeraccording to claim 1, wherein Het comprises a group selected fromoxadiazoles, thiadiazoles, pyridines, pyrimidines, and benzo-fusedanalogues thereof.
 4. A polymer according to claim 1 which comprises aluminescent polymer of general formula:

which is cross-linked, in which p, q and r are independently eachintegers in the range 1 to
 100. 5. A polymer according to claim 1,wherein Ar₁ comprises an aryl group.
 6. A polymer according to claim 1,wherein Ar₂ comprises an aryl group.